Producing Isotopically Enriched Plant, Soil Solution, and Rhizosphere Soil Materials over a Few Hours

There are scientific benefits for using an automated closed steady-state flow 13C (carbon; C) plant–soil labeling system (PSLS) for online recording and adjustment of 13CO2 (carbon dioxide) concentration equivalents to those used by photosynthesis, as compared to widely used uncontrolled open pulse labeling systems. Wheat plants were labeled at four growth stages (four leaves, tillering, late boot, and early dough) with 13CO2 for 2 and 6 h continuously. Analyses of the 13C/12C isotope using isotope ratio mass spectrometry of plant, soil solution, and rhizosphere soil samples showed that the injected 13CO2 was closely correlated with the 13C pools. The labeled 13C root exudates at tillering stage to rhizosphere soil increased from 0.4 ± 0.1 mg 13C pot−1 (four plants) after 2 h to 2.5 ± 1.0 mg 13C pot−1 after 6 h of labeling. The steady-state PSLS permits rapid control and maintenance of 13C by 13CO2 injection, enabling detailed examination of the C budget over short labeling periods.